Image forming apparatus with cleanable transfer roller

Abstract

A transfer roller is spaced away from the outer surface of a photosensitive drum by a specified distance to prevent the abrasion and damage of the photosensitive drum by the contact of the transfer roller and the photosensitive drum. The transfer roller not in contact with the photosensitive drum can be formed to have a sufficient hardness without damaging the outer surface of the photosensitive drum. Further, since the transfer roller has a sufficient hardness, cleaning blades can be held in without damaging the transfer roller with a sufficiently large force without damaging the transfer roller, thereby securely scraping off toner and the line adhered to the transfer roller and preventing the rear surface of a transfer sheet from being smeared.

What is claimed is:  
     
       1. An image forming apparatus, comprising: 
       a photosensitive body on which a toner image is to be formed;  
       a transfer roller spaced away from an outer surface of the photosensitive body by a specified distance for transferring a toner image formed on the photosensitive body to a sheet;  
       a transfer timing detector for detecting a non-image transfer period;  
       a transfer output applier for applying a transfer output to the transfer roller;  
       a transfer output setter, responsive to the transfer timing detector, for alternately setting a polarity of the transfer output, applied to the transfer roller by the transfer output applier, at positive and negative polarities during a detected non-image transfer period; and  
       a transfer output controller, responsive to the transfer output setter, for controlling the transfer output applier to apply the transfer output to the transfer roller at alternate polarities set by the transfer output setter thereby repelling toner having both polarities from the transfer roller.  
     
     
       2. An image forming apparatus according to claim  1 , further comprising a cleaning blade held in contact with the transfer roller for scraping off toner from the transfer roller, wherein the cleaning blade extends in a direction opposite to the rotating direction of the transfer roller. 
     
     
       3. An image forming apparatus according to claim  2 , further comprising another cleaning blade extending in the rotating direction of the transfer roller. 
     
     
       4. An image forming apparatus according to claim  1 , further comprising: 
       the photosensitive body having opposite sides;  
       the transfer roller having opposite sides; and  
       transfer wheels provided at the opposite sides of the transfer roller and having a diameter larger than that of the transfer roller, the transfer wheels contacting with outer surfaces of the opposite sides of the photosensitive body so as to define a space between the photosensitive body and the transfer roller.  
     
     
       5. An image forming apparatus according to claim  1 , wherein the transfer output setter sets the transfer output according to an apparatus installation environment condition during an image-transfer period. 
     
     
       6. An image forming apparatus according to claim  1 , wherein the transfer roller has a surface roughness of 10 μm or smaller. 
     
     
       7. An image forming apparatus according to claim  1 , wherein the cleaning blade is formed of a PET film. 
     
     
       8. An image forming apparatus according to claim  1 , wherein the transfer timing detector detects a transfer timing based on a position of a transfer sheet. 
     
     
       9. An image forming apparatus according to claim  1 , wherein the transfer output setter sets a single alternation of the polarity of the transfer output during each non-image-transfer period.